General Augusto Pinochet, the former Chilean dictator who presided over a 17-year reign of terror and ordered foreign assassinations, was arrested at a London hospital on Friday night by police acting on a request from Spain.

Pinochet, 82, was arrested at the London Bridge hospital on a warrant - an Interpol Red Notice - which alleges that between 1973 and 1983 he committed atrocities against Spanish citizens. He was held as he was convalescing after minor surgery to his back.

The news of Pinochet's seizure by Scotland Yard officers was greeted with euphoria by Chilean exiles and former victims of his torture. Among them was the former personal doctor of President Salvador Allende, who perished in Pinochet's coup. "It is a great triumph of justice," said Dr Oscar Soto. "Pinochet must now give account for more than 3,000 deaths, exiles and tortures in the 17 years of his dictatorship."

Pinochet's arrest is the culmination of a week of high-level police and diplomatic activity between London and Madrid. It is the first arrest of a former head of state travelling on a diplomatic passport on British soil.

The Spanish judges who requested his arrest had initially sought only to question Pinochet as part of an investigation into human rights violations in Chile and Argentina. But an international warrant was sworn after a warning from the British authorities that Pinochet was about to check out of the hospital and flee the country. The judges - who are now planning to travel to Britain to question him - have 40 days to put a case for extradition.

His arrest is the result of a year-long struggle by Madrid judges Baltasar Garzon and Manuel Garcia Castellon to have Pinochet brought to account for the brutality that followed his overthrow of the government of Allende.

Sources in Spain said the arrest was made after a warrant was issued on Friday by Garzon, Spain's leading investigative magistrate on charges of suspected 'genocide and terrorism'.

The net has been closing in on Pinochet since the summer when the US, which supported his regime, finally agreed to provide government documents to Castellon who launched his inquiry last year.

On Tuesday Castellon asked Britain to allow Spanish authorities to take a statement from Pinochet. On Wednesday Garzon asked Britain to detain Pinochet.

Garzon also wants to question him about Operation Condor, an organised plan of repression allegedly implemented by various Latin American dictatorships in the 1970s and 1980s.

The Chilean government, which opposes Spain's investigations, says Pinochet is under no obligation to testify because he travelled to London on a diplomatic passport.

In a statement issued in Oporto, Portugal, where Chilean President Eduardo Frei is attending the Ibero-American summit, the Chilean government said it was "filing a formal protest2 with London for what it considers a violation of diplomatic immunity.

Earlier this year Pinochet took up his seat as a life-long senator in Chile - a role he wrote into the country's constitution. As a senator, he is immune from prosecution under Chilean law.

His sudden arrest caught many on the hop, including Pinochet's old ideological enemy, Cuba's Fidel Castro. "Is it true? Is it confirmed?" the 72-year-old Communist leader asked in Oporto.